The invention relates to methods for operating a network and to networks embodied accordingly.
The significance of networks or network services has increased constantly in recent years. Besides their well-known use as a communications platform, such as the internet, their use in the industrial field is also of increasing significance, for instance in linked-together control or automation systems.
Especially in industrial applications, a reliable network connection among the individual participants that is as effective as possible, or in other words is fast and reliable, is of extreme importance, so as to avoid problems or even failures in production. To assure the most effective possible communication, the amount of data that must be exchanged or transmitted in the context of the communication must be as low as possible.
A communications system specified by ODVA and known by the name CPIsync employs clock time synchronization in all the secondary stations of a network that has a primary station and secondary stations. The system has a primary station and secondary stations. In addition to communication between the primary station and secondary stations, communication between secondary stations (so-called cross communication) is also provided. If one secondary station sends data to a further secondary station, it adds a time statement in the form of a clock time to the data to be transmitted; this time indicates when the transmitted data were refreshed. Data pertaining to a refreshment cycle time are also added. The receiver must always expect that the refreshment cycle time can change. Moreover, such communication is not limited to a fixed, constant cycle time. As a result, besides the actual data, further additional data must be transmitted, making the overall data transmission quite inefficient. Moreover, the receiver (consumer) of the particular data transmitted must keep an appropriate computation power available so that it can manage the change in cycle times.
Another communication method is known by the name SERCOS III. This communications system for networks which have a primary station and secondary stations does not, however, specify cross communication or in other words communication between the secondary stations. From this communications system, only communication between the primary station and the various secondary stations is contemplated. This communication plan proves to be relatively slow for certain applications.
In communication between the primary station and the secondary stations, a mechanism is specified in which the data refreshment rate of the transmitted data is specified by the primary station. In this connection, besides the communications cycle time, there is a so-called NC cycle time, which describes the cycle time with which the primary station refreshes its data to the secondary stations. Besides these two cycle times, there is a refreshment signaling in the data telegram from the primary station to each secondary station, in which the primary station signals when its transmitted data were refreshed (so-called “IPO sync bit”). From the refreshment signaling, the secondary stations can optimize their regulation and control algorithms and synchronize them with the NC cycle time.
For assuring reliable communication, the methods and systems described require a relatively large amount of time, which makes it difficult or impossible to use them in systems that require very fast connections, such as real-time systems.